The Innate Immune System provides the first line of defense against pathogens, and plays a critical role in controlling and instructing Adaptive Immunity. This interface was the topic of a highly successful Keystone Symposium that was held in January, 2001 as well as a series of Reviews, News and Views and Research Articles in journals such as Nature, and Science, in the past few years. In addition to having significance to responses to microorganisms, the topic is of major interest to scientists in other areas of immunology including Tumor Immunology, Autoimmunity and Vaccine Development. The meeting will highlight the new frontiers of research on the cells, receptors, signal transduction pathways, and soluble mediators of innate immunity that provide initial host responses and that control adaptive immunity. A multidisciplinary group oftop ranking researchers including molecular biologists, biochemists and cellular immunologists is invited to discuss emerging concepts, novel technologies and new avenues of research. This meeting will be especially rewarding for students and postdoctoral fellows in search of opportunities for future research and challenges.